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[LLD][COFF] Add support for CHPE code ranges metadata. #105741

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merged 1 commit into from
Aug 23, 2024
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[LLD][COFF] Add support for CHPE code ranges metadata. #105741

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16 changes: 16 additions & 0 deletions lld/COFF/Chunks.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1078,6 +1078,22 @@ void ECExportThunkChunk::writeTo(uint8_t *buf) const {
write32le(buf + 10, target->getRVA() - rva - 14);
}

size_t CHPECodeRangesChunk::getSize() const {
return exportThunks.size() * sizeof(chpe_code_range_entry);
}

void CHPECodeRangesChunk::writeTo(uint8_t *buf) const {
auto ranges = reinterpret_cast<chpe_code_range_entry *>(buf);

for (uint32_t i = 0; i < exportThunks.size(); i++) {
Chunk *thunk = exportThunks[i].first;
uint32_t start = thunk->getRVA();
ranges[i].StartRva = start;
ranges[i].EndRva = start + thunk->getSize();
ranges[i].EntryPoint = start;
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So this is a similar list as #105739, with the same start RVAs, but containing the size and not the destination? And the EntryPoint value seems pointless at this point, I presume it will seem more useful after some more future patches.

(I.e. I'm not questioning this patch, I'm questioning the usefulness of this data structure - but I guess it makes more sense when more complete.)

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I'm afraid it doesn't make more sense even when it's more complete. I've never seen StartRva and EntryPoint differ, even with some unusual synthetic inputs that I experimented with for custom export thunks. I’m not sure why it’s structured this way. Instead of duplicating the value in EntryPoint, I imagine it could store the redirection destination here and use a single structure instead of separate ones for redirection and code ranges.

As for how these structures are used, I can only speculate, so please keep in mind that this is just a guess. I think it might be useful for auxiliary IAT handling. The loader needs to populate the auxiliary IAT with addresses of actual ARM64EC functions, where something like redirection metadata could be used. It would also need to detect runtime patching of x86 thunks to know when to revert the auxiliary IAT to go through the call checker. For that, it would additionally need to know the thunks' sizes, which is what the code ranges metadata provides.

}
}

size_t CHPERedirectionChunk::getSize() const {
return exportThunks.size() * sizeof(chpe_redirection_entry);
}
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11 changes: 11 additions & 0 deletions lld/COFF/Chunks.h
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Expand Up @@ -749,6 +749,17 @@ class ECCodeMapChunk : public NonSectionChunk {
std::vector<ECCodeMapEntry> &map;
};

class CHPECodeRangesChunk : public NonSectionChunk {
public:
CHPECodeRangesChunk(std::vector<std::pair<Chunk *, Defined *>> &exportThunks)
: exportThunks(exportThunks) {}
size_t getSize() const override;
void writeTo(uint8_t *buf) const override;

private:
std::vector<std::pair<Chunk *, Defined *>> &exportThunks;
};

class CHPERedirectionChunk : public NonSectionChunk {
public:
CHPERedirectionChunk(std::vector<std::pair<Chunk *, Defined *>> &exportThunks)
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2 changes: 2 additions & 0 deletions lld/COFF/Driver.cpp
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Expand Up @@ -2444,6 +2444,8 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
ctx.symtab.addAbsolute("__arm64x_redirection_metadata_count", 0);
ctx.symtab.addAbsolute("__hybrid_code_map", 0);
ctx.symtab.addAbsolute("__hybrid_code_map_count", 0);
ctx.symtab.addAbsolute("__x64_code_ranges_to_entry_points", 0);
ctx.symtab.addAbsolute("__x64_code_ranges_to_entry_points_count", 0);
}

if (config->pseudoRelocs) {
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10 changes: 10 additions & 0 deletions lld/COFF/Writer.cpp
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Expand Up @@ -2071,6 +2071,12 @@ void Writer::createECChunks() {
replaceSymbol<DefinedSynthetic>(codeMapSym, codeMapSym->getName(),
codeMapChunk);

CHPECodeRangesChunk *ranges = make<CHPECodeRangesChunk>(exportThunks);
rdataSec->addChunk(ranges);
Symbol *rangesSym =
ctx.symtab.findUnderscore("__x64_code_ranges_to_entry_points");
replaceSymbol<DefinedSynthetic>(rangesSym, rangesSym->getName(), ranges);

CHPERedirectionChunk *entryPoints = make<CHPERedirectionChunk>(exportThunks);
a64xrmSec->addChunk(entryPoints);
Symbol *entryPointsSym =
Expand Down Expand Up @@ -2186,6 +2192,10 @@ void Writer::setECSymbols() {
pdata.first->getRVA());
}

Symbol *rangesCountSym =
ctx.symtab.findUnderscore("__x64_code_ranges_to_entry_points_count");
cast<DefinedAbsolute>(rangesCountSym)->setVA(exportThunks.size());

Symbol *entryPointCountSym =
ctx.symtab.findUnderscore("__arm64x_redirection_metadata_count");
cast<DefinedAbsolute>(entryPointCountSym)->setVA(exportThunks.size());
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4 changes: 2 additions & 2 deletions lld/test/COFF/Inputs/loadconfig-arm64ec.s
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Expand Up @@ -66,7 +66,7 @@ __chpe_metadata:
.word 1
.rva __hybrid_code_map
.word __hybrid_code_map_count
.word 0 // __x64_code_ranges_to_entry_points
.rva __x64_code_ranges_to_entry_points
.rva __arm64x_redirection_metadata
.rva __os_arm64x_dispatch_call_no_redirect
.rva __os_arm64x_dispatch_ret
Expand All @@ -75,7 +75,7 @@ __chpe_metadata:
.rva __os_arm64x_check_icall_cfg
.word 0 // __arm64x_native_entrypoint
.word 0 // __hybrid_auxiliary_iat
.word 0 // __x64_code_ranges_to_entry_points_count
.word __x64_code_ranges_to_entry_points_count
.word __arm64x_redirection_metadata_count
.rva __os_arm64x_get_x64_information
.rva __os_arm64x_set_x64_information
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9 changes: 7 additions & 2 deletions lld/test/COFF/arm64ec-export-thunks.test
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Expand Up @@ -58,7 +58,10 @@ EXP-CHPE: CodeMap [
EXP-CHPE-NEXT: 0x1000 - 0x100C ARM64EC
EXP-CHPE-NEXT: 0x2000 - 0x3020 X64
EXP-CHPE-NEXT: ]
EXP-CHPE-NEXT: CodeRangesToEntryPoints: 0
EXP-CHPE-NEXT: CodeRangesToEntryPoints [
EXP-CHPE-NEXT: 0x3000 - 0x3010 -> 0x3000
EXP-CHPE-NEXT: 0x3010 - 0x3020 -> 0x3010
EXP-CHPE-NEXT: ]
EXP-CHPE-NEXT: RedirectionMetadata [
EXP-CHPE-NEXT: 0x3000 -> 0x1000
EXP-CHPE-NEXT: 0x3010 -> 0x1000
Expand Down Expand Up @@ -121,7 +124,9 @@ ENTRY-CHPE: CodeMap [
ENTRY-CHPE-NEXT: 0x1000 - 0x100C ARM64EC
ENTRY-CHPE-NEXT: 0x2000 - 0x2010 X64
ENTRY-CHPE-NEXT: ]
ENTRY-CHPE-NEXT: CodeRangesToEntryPoints: 0
ENTRY-CHPE-NEXT: CodeRangesToEntryPoints [
ENTRY-CHPE-NEXT: 0x2000 - 0x2010 -> 0x2000
ENTRY-CHPE-NEXT: ]
ENTRY-CHPE-NEXT: RedirectionMetadata [
ENTRY-CHPE-NEXT: 0x2000 -> 0x1000
ENTRY-CHPE-NEXT: ]
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4 changes: 3 additions & 1 deletion lld/test/COFF/arm64ec-patchable-thunks.test
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Expand Up @@ -34,7 +34,9 @@ PATCH-CHPE: CodeMap [
PATCH-CHPE-NEXT: 0x1000 - 0x1008 ARM64EC
PATCH-CHPE-NEXT: 0x2000 - 0x2010 X64
PATCH-CHPE-NEXT: ]
PATCH-CHPE-NEXT: CodeRangesToEntryPoints: 0
PATCH-CHPE-NEXT: CodeRangesToEntryPoints [
PATCH-CHPE-NEXT: 0x2000 - 0x2010 -> 0x2000
PATCH-CHPE-NEXT: ]
PATCH-CHPE-NEXT: RedirectionMetadata [
PATCH-CHPE-NEXT: 0x2000 -> 0x1000
PATCH-CHPE-NEXT: ]
Expand Down
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